1. Field of the Invention
The present invention relates to materials processing and, more particularly, relates to welding components.
2. Related Art
Welding tungsten components to other tungsten components to form an assembly generally is not considered to be feasible because the welding operation itself causes severe recrystallization of the tungsten adjacent to the melted area, i.e., the weld, between and formed by the components. This recrystallization of the tungsten causes the tungsten components to become brittle and results in a weak bond. As used herein, the term "tungsten component" refers to components composed of tungsten, alloys of tungsten, tungsten alloys including a solid suspension, tungsten including a solid suspension, or any combination of materials including tungsten.
It is known to join tungsten components to other tungsten components by brazing. Particularly, the tungsten components are aligned and held in contact at a location where a bond is to be formed. The brazing metal is then melted at the location where the bond is to be formed. The brazing metal, however, typically has a lower melting temperature than the melting temperature of tungsten. As a result of the difference between the melting temperature of the brazing metal and the tungsten, a strong bond between the tungsten components and the brazing metal is not present when the components, in operation, are subjected to elevated temperatures near the braze material melting point. Brazing techniques, therefore, do not provide sufficient bond strength between the tungsten components at elevated temperatures close to the brazing material melting point. The brazing metal may also be a source of contamination in some applications.
Problems associated with welding tungsten components to other tungsten components are amplified when the tungsten components to be welded are an electrode, such as an anode, and a lead. The term "lead", as used herein, refers to an electrical conductor for conducting electricity to an electrode. The end portion of the lead which is to be bonded to the end portion of the anode typically has a very small diameter. The lead, for example, has a diameter of 0.0165 inches and the anode has a diameter of 0.040 inches. Providing a strong bond between such small working areas is very difficult.
To overcome these problems, a method for forming an anode-lead assembly by melting back the end of a lead can be utilized. The end of the lead typically is melted with a tungsten-inert-gas (TIG) welder. When the end of the lead is melted, a spherical-shaped portion having a larger diameter than the other portion of the lead is formed. Particularly, when the tungsten is melted, the melted tungsten forms into the spherical-shape due to surface tension. The spherical-shaped portion serves as an anode. In the TIG operation, it is difficult to control the diameter of the anode, i.e., the diameter of the spherical-shaped portion, being formed. Further, in some applications, the spherical-shape of the anode is unsatisfactory such as too large or of undesirable shape. For example, it may be preferred that the anode be bullet-shaped or conically-shaped.
One known technique to shape the anode formed by the TIG process is commonly referred to as electrical discharge machining (EDM). Particularly, subsequent to a TIG process, EDM techniques are used to cut the desired anode shape from the spherical-shaped portion of the melted lead. EDM techniques, however, typically require tens of minutes to complete and are too slow to be cost effectively used in mass production of such assemblies. Other techniques for shaping the anode such as machining and etching also require too much time and result in waste.
It is therefore an object of the present invention to provide a method for welding tungsten components so that a strong bond is formed between the components.
Another object of the present invention is to provide a method for welding tungsten components which does not result in damage to the components during the welding process.
Still another object of the present invention is to provide a method for welding a tungsten anode to a tungsten lead.
Yet another object of the present invention is to provide a method for welding tungsten components which facilitates mass production of welded tungsten assemblies.